Stop nutsedge; observe before pruning

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February 8, 2013
: Updated: February 8, 2013 4:37pm

Q.﻿﻿﻿ We had a terrible problem with nutgrass in our lawn last summer. Will a pre-emergent weedkiller stop it this year? If so, which one and when should it be applied?

A. The weed you have isn't a true grass but a sedge. You can distinguish sedges by rolling the plant's stem between your thumb and index finger. Grasses will have round stems. Sedges will be triangular.

Sedges are perennials — they come back from their roots. Pre-emergents work only on annual weeds as their seeds try to germinate. So if nutsedge is your biggest concern, you would be wasting the pre-emergent. You'll want to use either Image or Sedgehammer after the nutsedge is up and growing actively. That's generally mid-May through mid-September.

Q. Should trees (5- to 15-year-old, red oak and pecan) that were sparse in leaf count in 2012 be pruned to encourage new growth this spring? We have perhaps 100 trees that would fit into that category on some property we own.

A. That's a lot of work with no guarantee it will help. You'd be better advised to apply an all-nitrogen fertilizer to them in mid- or late March and to keep them watered deeply. Evaluate them later this year to determine which need to be pruned, which can stand on their own and which need to be taken out.

Q. I have a Texas Everbearing fig tree. When should I feed it, with what and how much?

A. Texas A&M fruit specialists recommend no major feeding or pruning of figs. Both encourage strong vegetative growth, which will come at the expense of fruit production. It will get enough nutrients from the soil, especially if plants near it are being fed.

Q. I have red oak roots growing toward my slab foundation. If I cut down the trees, how long does it take for roots to die or stop growing?

A. Hopefully there is a better solution than removing the trees. Red oaks are valuable landscaping commodities across Texas. If the trees are 8 or 9 feet or farther from the house, you should be able to cut a trench across their roots and install a root barrier. Vinyl pond liners stop the growth of roots efficiently.

If you do decide that you need to remove the tree, root growth will stop the moment the tree is removed. I hope you won't have to resort to that.

Q. My medium-size pecans are dropping many of their branches. It appears some type of insect or ant has dug back into the branch and caused it to be weaker. As a result, the pecans haven't borne many fruit. What can I use to kill the insects so I'll have pecans in future years?

A. It sounds like twig girdlers, not ants, are the culprits. They're large beetles with long antennae that extend back over their backs. The females deposit their eggs in the parts of the branches that will ultimately fall. Then they move a bit farther back up the affected branches, where they score the twigs and small limbs with their sharp mouthparts. The branches die and fall to the ground (as you described), and the larvae develop within the decaying tissues.

Unfortunately, the adult insects never feed on the twigs, so spraying is impractical. The larvae develop within the branches, so they're sequestered from any treatment you might apply. Rake up the fallen branches and destroy them. You'll reduce the populations, although they will return from other trees in the neighborhood.

Q. I'd like to find a durable deciduous tree that grows taller than it does wide. It will need to tolerate our local soils. I was thinking about sycamores. Do you have anything better?

A. Cedar elms are probably the best choice for most of Texas. Similarly, chinquapin oaks grow to 40 or 50 feet tall and 40 or 45 feet wide as they mature in several decades. Sycamores have a couple of insect and disease problems that score them down, although the trees are pretty. They're also somewhat messy as their huge leaves drop from midsummer on.

All of these trees broaden as they mature, but by then the branches are quite high.